Hardmetal composites inlays and hardfacings are used as cutting edges and wear surfaces in drill bits and other earth-engaging equipment. Hardmetal composites generally consist of a hardmetal such as tungsten carbide, diamond, cubic boron nitride, or ceramic dispersed in a softer, metal matrix, optionally including a binder metal as well.
Tungsten carbide (or carbide) is a hardmetal frequently chosen for hardfacing abrasive and cutting surfaces on drill bits. Enhanced performance can be achieved with high carbide loading (high volume fraction) and large constituent particles. At higher carbide volume fraction and greater particle sizes, hardness is increased. However, during forge densification, the carbide particles are more likely to come into contact with one another, creating increased porosity and forming bridges susceptible to cracking and particle fracture. Composites that include carbide particles with lower hardness and/or smaller particle size can increase the loading threshold for these defects, but with attendant sacrifice in wear performance.
Designs that increase abrasiveness, such as high hardphase volume fraction and large particle size, often suffer lack of resistance to impact. Thus, there seems to be an inherent trade-off between hardness and toughness in the manufacture of hardfacing materials, limiting levels of achievable hardphase volume fractions. Prior art suggests that carbide hard phase volume fractions cannot exceed about 40 vol % to 60 vol %, without suffering the attendant defects just described.
Prior art solutions that have most nearly achieved high hardphase volume fractions while maintaining impact resistance have addressed the influence of matrix microstructure on deformation mechanics of hard composites affecting toughness and wear progressions in drilling service. U.S. Pat. No. 6,045,750 discloses a powder-forging method producing hard composite coatings that achieve sintered cemented carbide loading values over about 75 vol %. However, these coatings are rough and limited in thickness to about 3× particle diameter. For thicker hard composites, full-density powder forge fabrication is limited to formulations with hardphase volume fractions of 45 vol % or less, depending on forging pressure and temperature.
Thus, a need exists for hard metal composites to be used as cutting edges and wear surfaces in drill bits and other earth-engaging equipment, which composites achieve high particle size and a hardphase volume fraction higher than prior art achievement, without sacrificing toughness.